1. Field of the Invention
The present invention relates to an improved multi-core rotary circular die of the type designed for producing multi-layer tubular film.
2. Description of the Prior Art
Heretofore, circular dies of various constructions have been proposed, such as, for example, multi-core rotary circular dies which are composed of a body having a plurality of inlets for molten resins, an inner core having resin feeding passages formed by a plurality of pipes communicating with the resin inlets, cores having spherical seal type resin passages connected to the resin feeding pipes and cylindrical parts on spherical parts of the multiple cores which are fitted at the spherical parts to each other, whereby lips are formed, to offer adjustable thickness between the cylindrical parts.
However, in the conventional technology, where a plurality of pipes are formed in the inner core by a screwIng manner or the like, the following disadvantages have been found:
AN INNER SIZE OF THE MOLTEN RESIN PASSAGE IS LARGE; THE MOLTEN RESIN ADHERES ON THE OUTER AND INNER SURFACES OF THE PIPES OF THE MOLTEN RESIN PASSAGE TO CAUSE RESIDENCE OF THE RESIN; IT TAKES A LONG TIME FOR DISASSEMBLY AND CLEANING; AND THE UTILITIES OF AIR FOR INFLATION AND WATER FOR COOLING A MOLTEN RESIN FILM CAN BE FED BY CONNECTING ROTATABLE JOINTS AT THE END OF THE ROTARY SHAFT.
However, it has been relatively difficult to feed electric power through a slip ring to the rotatable part, as it is difficult to provide continuous rotation of the die without the slip ring and it is necessary to provide a reciprocating turn, whereby the equipment and the operation are complicated.